The present disclosure relates to identifying aerobic activity within the heart muscle (myocardium) and, more particularly, to measuring changes in intra-myocardial oxygen saturation during cardiac surgery.
During heart surgery, patients placed on cardiopulmonary bypass typically undergo myocardial protection through the administration of cardioplegia solution and myocardial cooling. Such a procedure reduces or arrests aerobic and metabolic activity, including contractions, within the myocardium (protected cardiac arrest). Metabolic arrest avoids ischemic damage, prevents the accumulation of toxic metabolites and aims to alleviate post-operative inflammation and dysfunction. While there is a general presumption that intra-myocardial metabolic and aerobic activity is largely arrested during protected cardiac arrest, there is currently no practical and sensitive manner to determine this.
As a result, repeat administration of cardioplegia solution for ongoing myocardial protection is empiric at best, and often only when spontaneous myocardial electrical activity is appreciated. This lack of insight into the metabolic and aerobic activity may result in inadequate myocardial protection. A need thus exists for a method to effectively measure metabolic and aerobic activity within the myocardium during times of presumed adequate protection during a surgical intervention. The method described in this disclosure would improve the assessment of intra-myocardial metabolic and aerobic activity and would be vital to transforming the processes used to adequately protect the myocardium during such surgical procedures.
The present disclosure relates to the use of a conventional photonic needle in the myocardium to measure real time changes in myocardial tissue oxygen saturation. One such photonic needle is able to determine various tissue characteristics based on the absorption of a given spectrum of applied light, including the measurement of tissue oxygen saturation. The decrease in intra-myocardial oxygen saturation during protected cardiac arrest is indicative of low-grade, but ongoing aerobic processes (i.e. metabolic activity). With a better understanding of changes in myocardial oxygen saturation during protected cardiac arrest, alterations in cardioplegia administration strategies may be implemented to better protect the myocardium, increase the amount of time the surgeon has to perform the operation, improve subsequent cardiac function, and decrease recovery time after surgery.
According to an illustrative embodiment of the present disclosure, a method includes the steps of inserting a distal end of a photonic needle into myocardium, emitting light from the distal end of the photonic needle within the myocardium, and detecting light reflected from the myocardium. The method also includes the steps of processing the reflected light to determine intra-myocardial oxygen saturation. This will, in turn, provide the assessment of the baseline metabolic state of the myocardium.
According to an illustrative embodiment of the present disclosure, a method is provided for measuring oxygen saturation in the myocardium. The method includes the step of inserting a photonic needle within the myocardium, wherein the photonic needle includes a shaft, a first optic fiber extending within the shaft and coupled to a light source, and a second optic fiber extending within the shaft and coupled to a light detector. The method further includes the steps of emitting light from the first optic fiber, collecting light with the second optic fiber, obtaining spectroscopic data from light delivered and collected from the myocardium via the photonic needle, and processing the spectroscopic data to measure oxygen saturation in the myocardium. A further step will include detecting myocardial metabolic activity based upon changes in the measured oxygen saturation of the myocardium.
The illustrative method of the present disclosure utilizes the photonic needle to measure changes in myocardial tissue oxygen saturation levels during periods of protected cardiac arrest, where as previously defined, protected cardiac arrest is understood to be the cessation of cardiac contraction and electrical activity induced typically after aortic cross clamp, myocardial cooling, and cardioplegia administration. As such, there is a presumption that myocardial tissue oxygen saturation should remain constant (i.e. no utilization of oxygen), or decline very gradually over time. If the above presumption is not borne out (i.e. a rapid decline in myocardial oxygen saturation), this method would allow clinicians to monitor those changes in myocardial oxygen saturation in real-time, and alter myocardial protective strategies accordingly (as this would indicate ongoing metabolic activity in an ischemic environment that would result in more tissue damage). With improved understanding of the changes in myocardial oxygen saturation during protected cardiac arrest, alterations in cardioplegia composition and administration strategies may be used to better protect the myocardium, increase the amount of time that the surgeon has to perform the operation, improve subsequent cardiac function, and decrease recovery time after surgery.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.